In order to provide multi-channel voice/data communications over a broad geographical area, wireless (e.g. cellular) communication service providers currently install transceiver base-stations in protected and maintainable facilities (e.g. buildings). Because of the substantial amount of hardware currently employed to implement the signal processing equipment for a single cellular channel, each base-station is typically configured to provide multichannel communication capability for only a limited portion of the frequency spectrum that is available to the service provider. A typical base-station may contain three to five racks of equipment which house multiple sets of discrete receiver and transmitter signal processing components in order to service a prescribed portion (e.g. 48) of the total number (e.g. 400-30 KHz) channels within an available (e.g. 12 MHz) bandwidth.
The receiver section of a typical one of a basestation's plurality (e.g. 48) of narrowband (30 KHz) channel units is diagrammatically illustrated in FIG. 1 as comprising a dedicated set of signal processing components, including a front end, down-conversion section 10, an intermediate frequency (IF) section 20 and a baseband section 30. Front end section 10 is comprised of a low noise amplifier 11 to which the transceiver site's antenna is coupled, a radio frequency-to-intermediate frequency (RF-IF) down-converting mixer 13 and an associated IF local oscillator 15, while IF section 20 is comprised of a bandpass filter 21 to which the output of mixer 13 is coupled, an amplifier 23, an IF-baseband mixer 25 and an associated baseband local oscillator 27. Bandpass filter 21 may have a bandwidth of 100 KHz centered at a respective one of the 400-30 KHz sub-portions of a 10 MHz wide cellular voice/data communication band, diagrammatically illustrated in the multi-channel spectral distribution plot of FIG. 2.
Baseband section 30 contains a lowpass (anti-aliasing) filter 31, an analog-to-digital (A-D) converter 33, a digital (demodulator/error correction) processing unit 35, and an associated telephony (e.g. T1 carrier) unit 37 through which the processed channel signals are coupled to attendant telephony system equipment. The sampling rate of the A-D converter 33 is typically on the order of 75 kilosamples/sec. The narrowband channel signal as digitized by A-D converter 33 is demodulated by processing unit 35 to recover the embedded voice/data signal for application to telephony carrier unit 37. (A similar dedicated signal processing transmitter section, complementary to the receiver section, is coupled to receive a digital feed from the telephony system equipment and output an up-converted RF signal to the transceiver site's antenna.)
For a typical urban service area, in order to optimize service coverage within the entire bandwidth (e.g. 10-12 MHz) available to the service provider and to ensure noninterfering coverage among dispersed transceiver sites at which the base-stations are located, the transceiver sites are customarily geographically distributed in mutually contiguous hex-cells (arranged in a seven cell set). Thus, each cell has its own limited capacity multi-rack basestation that serves a respectively different subset of the available (400) channels, whereby, over a broad geographical area, the frequency allocation within respective cells and the separation between adjacent cell sets may be prescribed to effectively prevent mutual interference among any of the channels of the network.
It will be readily appreciated that, since every channel has components spread over multiple equipment racks, such as those that make up a typical channel receiver section described above with reference to FIG. 1, the cost and labor in geographically situating, installing and maintaining such equipment are not insubstantial. Indeed, the service provider would prefer to employ equipment that would be more flexible both in terms of where it can be located and the extent of available bandwidth coverage that a respective transceiver site can provide. This is particularly true in non-urban areas, where desired cellular coverage may be concentrated along a highway, for which the limited capacity of a conventional 48 channel transceiver site would be inadequate, and where a relatively large, secure and protective structure for the multiple racks of equipment required is not necessarily readily available.